1. Field of the Invention
The present invention relates to an endoscope including a picture image freeze device, and more particularly to improvement in the quality of a frozen picture image in an endoscope.
2. Description of the Background Art
In a conventional endoscope, a frame of picture image composed of odd and even fields is simultaneously obtained by using a color camera device such as a CCD during the operation of the endoscope.
When a frozen picture image is reproduced by the frame of picture, usually, a light pulse or pulsed light is irradiated to an object to be observed, extending over the boundary between the adjacent two fields, i.e. odd and even fields in order to reduce the discord or disagreement of the reproduced picture images due to the time difference between the two fields, as schematically shown in FIG. 1, wherein a VD signal represents a TV vertical synchronization drive signal.
However, when an object is moved during the operation, and a light pulse having a long pulse width is used, there happens the discord or disagreement between the picture images of the odd and even fields. Hence, when the picture image is reproduced in such a discord or disagreement situation, a flicker is caused in the reproduced picture image, which is troublesome and hard to observe the picture image.
In turn, when the pulse width of the light pulse is small, the flicker to be caused by the moving of the object is prevented, but a slight shift of timing for emitting the light pulse or a deformation of a wave form of the light pulse can readily vary the ratio of illuminance between the odd and even fields to cause a flicker.
In another conventional endoscope, a frozen picture image is reproduced by using the picture image of one of the odd and even fields. However, in such a case, although the flicker can be effectively prevented, the inherent resolving power provided in an endoscope of this kind is reduced by half.